Some of the information set forth herein has been published. See Pyle, A. M. and Barton, J. K., Mixed Ligand Complexes and Uses Thereof as Binding Agents to DNA, Inorganic Chemistry, 1987, 26:3820-3823, which was distributed by the publisher on November 6, 1987.
Throughout this application various publications are referenced by arabic numerals within parentheses. Full citations for these publications may be found at the end of the specification immediately preceding the claims. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.
There has been considerable interest in elucidating those factors which determine affinity and selectivity in binding of small molecules to DNA. (22-28) A quantitative understanding of such factors which determine recognition of DNA sites would be valuable in the rational design of sequence-specific DNA binding molecules for application in chemotherapy and in the development of tools for biotechnology. Much work has focused on the elucidation of non-covalent interactions with DNA by small natural products and their synthetic derivatives. (23-28) These small molecules are stabilized in binding to DNA through a series of weak interactions, such as the .pi.-stacking interactions assocatied with intercalation of aromatic heterocyclic groups between the base pairs, and hydrogen bonding and Van der Waals interactions of functionalities bound along the groove of the DNA helix. It would be valuable to understand quantitively the contributions from these different modes to stabilization of the bound complex at a DNA site.
Previous work has focused on the examination of non-covalent interactions with DNA of transition metal complexes of phenanthroline. (22, 29-32) The cationic complexes has been found both to intercalate into DNA and to bind non-covalently in a surface-bound or groove-bound fashion. These interactions with DNA have been characterized largely through spectroscopic and photophysical studies, and determinations of enantiomeric selectivities associated with binding by the metal complexes have been helpful also in establishing models. (29, 30) On the basis of these investigations, intercalation likely occurs preferentially from the major groove of the DNA helix and is favored for the .DELTA. isomer into a right-handed helix. In the case of the surface-bound interaction, it likely occurs along the minor groove of the helix and it is the .LAMBDA. isomer which is favored in surface-binding to right-handed DNA helices. FIG. 5 illustrates models for these binding interactions.
Based upon these binding interactions, derivatives of tris (phenanthroline) complexes have been developed which recognize selectively different conformations of DNA. By matching shapes and symmetries of the metal complexes to those of DNA conformations, probes for A-and Z-DNA have been designed. (31) Most recently, a diphenylphenanthroline complex of rhodium (III) has been found to induce double-stranded cleavage at cruciform sites upon photoactivation. (32) Although these complexes lack hydrogen bonding donors and acceptors and therfore must be associating with the DNA only through a mixture of Van der Waals and intercalative interactions, a high level of specificity is associated with the recognition of different DNA sites by these complexes.
The present invention involves mixed ligand complexes and complexes having three phenanthrenequionediimine ligands. The mixed ligand complexes of ruthenium (II) were explored for their interactions with B-DNA using a variety of biophysical and spectroscopic methods. Mixed ligand complexes of phenanthroline, phenanthrenequinonediimine, and derivatives thereof have been found to be useful for the construction and characterization of DNA-binding molecules. The ruthenium (II) complexes are particularly useful owing to their intense optical absorption and emission, their relative ease of preparation, and their inertness to substitution and racemization. (33-35)